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HYDRANAL® Videos
Volumetric Titration with Composite Reagent
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Karl Fischer Video on Volumetric Titration Using One-Component HYDRANAL®-Composite Reagent. Video shows:(1) Filling and conditioning the titration cell, (2) How to administer samples – solids, non-homogeneous products, and liquid samples.
The various titration steps for this method are described below the video.
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Titration Steps:
Addition of Reagent
The burette is filled with HYDRANAL®-Composite, i.e. the stock vessel. It is imperative that the burette, stock vessel and their interconnection be absolutely dry. Residual water can cause local changes in the titre and lead to errors in the results. Stock vessels are protected from atmospheric moisture by the addition of drying tubes.
Addition of Solvent
Depending on the size of titration cell and on the size of the sample to be investigated, 20-40 mL of HYDRANAL®-Methanol dry, HYDRANAL®-Methanol Rapid or HYDRANAL®-CompoSolver E are added to the titration vessel. The titration cell is closed immediately after the addition in order to keep the intrusion of atmospheric moisture to a minimum.
Pre-titration
The solvent in the titration vessel is then slowly titrated to dryness with the reagent. This "pre-titration" removes not only the residual water that was in the solvent, but also the adherent moisture in the cell, on the walls of the cell and the electrode. The atmosphere of the cell is also dried of moisture. The pre-titration must be carried out very carefully as any error will influence the subsequent determination of the water content of the sample. A titration to a stable end point is the prerequisite for a reliable analysis. A perfectly dried titration cell has a maximum drift consumption of 0.01 mL of KF reagent per minute.
Weighing the Sample
A pre-determined quantity of the sample to be investigated is administered to the pre-dried working medium. The cell is opened for as short a time as necessary and then closed again immediately after the sample was added.
Titration of the Water Content
 The titration should be started immediately. The dosing rate of the titration agent should be adjusted to the amount of water likely to be present. The initial stages of the titration should be rapid. The titration rate must be reduced when the end point is near. Modern instrumentation automatically adjusts the titration rate to the amount of water still remaining in the titration vessel.
Generally, one titrates to an end point of 10 seconds stability. A stable end point is a significant indication of the course of a titration with no complications. A vanishing end point indicates the water of the sample is released slowly or there is an interference by a side reaction.
Replacement of the Reagent
Following the completion of a titration, the spent solutions should be removed from the titration cell. Usually the titration cell is immediately re-filled with fresh solvent and dehydrated by a pre-titration. For "sequential titrations", the solvent mixture of the previous titration is immediately used as the working medium for the titration of the next sample. In this way, the use of a fresh solvent and a pre-titration for each titration is not required. When performing ‘sequential titrations’ the substance being investigated should be the same type. Furthermore, it must be ensured that the methanol content in the working medium does not fall below 25% as otherwise the end point can be shifted.
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